1. Field of the Invention
The present invention is directed to a process for preparing a homopolymer of xcex1-olefin or a copolymer of xcex1-olefin with other xcex1-olefins, having high hydrogen sensibility, high catalyst activity, and high polymer stereoregularity together with wide molecular weight distribution of xcex1-olefin polymers, by using a novel combination of organosilicon compounds having the specific molecular structure as one of the catalyst constituents: The invention also relates to the xcex1-olefin polymers (including homopolymers and copolymers) prepared by said process and the novel combination of organosilicon compounds as the catalyst constituent used for said process. The xcex1-olefin polymers prepared by said process has a high viscoelasticity and thus an excellent film-moldability ; furthermore, an injection-molded product is free from the problem relating to poor external appearance such as flow marks.
2. Description of the Related Art
In recent years, in JP-A-57-63310, JP-A-58-83016, JP-A-59-58010, JP-A-60-44507 and others, there have been proposed, for polymerization of xcex1-olefin, a number of highly active carrier-supported type catalyst systems comprising solid constituents containing indispensably magnesium, titanium, a halogen element and an electron donor, an organometal compound of a metal of I-III groups in Periodic Table, and an electron donor. Further, in JP-A-62-11705, JP-A-63-259807, JP-A-2-84404, JP-A-4-202505 and JP-A-4-370103, there have been disclosed other polymerization catalysts characterized by containing a specific organosilicon compound as an electron donor.
However, propylene polymers prepared by using a carrier-supported type catalyst system containing said organosilicon compound are generally having a narrow molecular weight distribution, and a low viscoelasticity when said polymers are melted. For those reasons such polymers often show defects in the molding properties as well as external appearances of the molded products, depending upon the applications thereof. In order to improve these defects, there have been proposed some methods in JP-A-63-245408, JP-A-2-232207 and JP-A4-370103, to spread the molecular weight distribution of polymer by polymerizing propylene in plural numbers of polymerization vessels, or by multiple-stage polymerization.
However, such methods require complicated operations, and the production speed should be inevitably lowered, thus, those methods are not industrially preferable due to the problems inclusive of production cost. Furthermore, in case of preparing a propylene polymer having a low molecular weight and a broad molecular weight distribution by using a plural number of polymerization vessels, a polymer having a low molecular weight should be prepared by use of an excessive amount of a chain transfer agent, for example hydrogen gas, in one of the polymerization vessels, resulting in higher polymerization pressure. Since the polymerization temperature should be lowered in case of a polymerization vessel which inevitably has a limitative pressure resistance, such method may cause adverse effects to the production speed.
Additionally, in JP-A-8-120021, there is disclosed a process for polymerization of an xcex1-olefin by using, as the constituent of catalyst, an alkyl cyclic aminosilane compound represented by the general formula R1Si(OR2)2R3 (wherein R1 is an alkyl group, and R3 is a cyclic amino group). However, only compounds whose R1 is methyl group are disclosed as the illustrative compounds of the alkyl cyclic aminosilane compounds. Moreover, it is quite silent as to the molecular weight distribution of the propylene polymers thus prepared by using those compounds as the constituent of catalyst.
Further, in JP-A-8-143621, there is disclosed a process for polymerization of an xcex1-olefin by using a bis cyclic aminosilane compound having two cyclic amino groups on the silicone atom specifically disclosed therein. Specifically disclosed this cyclic compound is a bis aminosilane compound having two single ring piperidino groups as cyclic amino groups. Similar to the above, there is no concrete description as to the molecular weight distribution of the propylene polymers prepared by use of said compounds as the constituent of catalyst.
Further, in EP-A-410443, there is disclosed bis(4-methylpiperidyl)dimethoxysilane usable for a process for polymerizing an xcex1-olefin. However, there is no concrete description as to the molecular weight distribution of a poly-xcex1-olefin obtainable therefrom, either.
Further, in JP-A-7-90012 and JP-A-7-97411, there are disclosed processes for polymerization of an xcex1-olefin by use of a silane compound having the substituent of nitrogen atom-containing heterocyclic group, wherein any one of carbon atoms in the heterocyclic structure is bonded directly to the silicon atom. However, there are no concrete description relating to the molecular weight distribution of the polymers prepared by using said compound.
On the other hand, it is proposed that a propylene polymer having broad molecular weight distribution and high crystallizability can be obtained by means of melt-mixing in the predetermined ratio, a propylene polymer having low molecular weight and high crystallizability with a propylene polymer having high molecular weight and high crystallizability; each one of those propylene polymers as the starting materials having been prepared by conventional processes before the melt-mixing. However, in case that molecular weight of a propylene polymer having low molecular weight is very different from that of a propylene polymer having high molecular weight, it is practically very difficult to run the melt-mixing operation of a propylene polymer of low molecular weight with a propylene polymer of high molecular weight, and it may cause the formation of gels and the deterioration of impact strength in thus obtained polymers as another problem.
The inventors of the present invention proposed a method of preparing propylene polymers having a wide molecular weight distribution by using as a catalyst a specific organosilicon compound containing polycyclic amino group in EP-A-841348 (JP-A-10-218926). In this method, though hydrogen is needed to coexist with a polymerization system as a chain transfer agent in order to adjust molecular weight of xcex1-olefin polymers, the polymerization system has a low hydrogen sensibility. Therefore, it is necessary to use a great amount of hydrogen in order to prepare xcex1-olefin polymers having a low molecular weight.
Where a great amount of hydrogen is introduced into a polymerization vessel, a pressure in the polymerization vessel becomes high. Since the polymerization vessel has a limitative pressure resistance, the polymerization temperature should be lowered, thus causing adverse effects to the production speed.
Further, it may be strongly demanded that xcex1-olefin polymer products obtained by an injection molding has less appearance defects (e.g., flow mark). However, the demand has not been met depending on the conditions.
It is an object of the present invention to provide a method of preparing an xcex1-olefin polymer having high stereoregularity and wide molecular distribution, using a high active and high hydrogen sensible catalyst system.
It is another object of the present invention to provide a method of preparing an xcex1-olefin polymer, an injection molding product of which has less appearance defects (e.g., flow mark).
The first aspect of the present invention relates to a method for preparing an xcex1-olefin polymer comprising the step of polymerizing or copolymerizing an xcex1-olefin in the presence of a catalyst which contains a solid catalyst constituent (A) which contains magnesium, titanium, a halogen element and an electron donor, an organoaluminum compound constituent (B), an organosilicon compound constituent (C) represented by the following general formula (4) and an organosilicon compound constituent (D) represented by the following general formulas (5) or (6) to prepare an xcex1-olefin polymer
RnSi(OR)4xe2x88x92nxe2x80x83xe2x80x83(4)
(wherein R is a hydrocarbon group having 1 to 8 carbon atoms, n is integer of 1 or 2) 
(wherein R1 is a hydrocarbon group having 1 to 8 carbon atoms, R2 is a hydrocarbon group having 1 to 8 carbon atoms, a hydrocarbylamino group having 2 to 24 carbon atoms, or a hydrocarbylalkoxy group having 1 to 24 carbon atoms, R3N is a polycyclic amino group having 7 to 40 carbon atoms, wherein the carbon atoms and the nitrogen atom form a cyclic skeleton).
In the said method, a mixture of the constituent (C) and the constituent (D) can be employed as an organosilicon compound used either in the prepolymerization or in the main polymerization, or both in the prepolymerization and in the main polymerization. Further, a mixture of the constituent (C) and the constituent (D) can be employed as an organosilicon compound used in the main polymerization after the prepolymerization with the constituent (C). Also, a mixture of the constituent (C) and the constituent (D) can be employed as an organosilicon compound used in the prepolymerization followed by the main polymerization with the constituent (D).
In the said method, it is preferred that said polymerizing or copolymerizing an xcex1-olefin comprises the steps of prepolymerizing an xcex1-olefin in the presence of a catalyst containing said solid catalyst constituent (A), said organoaluminum compound constituent (B), and said organosilicon compound constituent (C); and main polymerizing or copolymerizing an xcex1-olefin by adding said organosilicon compound constituent (D) to prepare an xcex1-olefin polymer.
In the said method, it is preferred that an amount of the organosilicon compound constituent (C) in the polymerization is 0.1 to 10 in terms of atomic ratio (Si/Ti) of silicon atom of the constituent (C) to titanium atom of the constituent (A), and 0.01 to 2 in terms of atomic ratio (Si/Al) of silicon atom of the constituent (C) to aluminum atom of the constituent (B).
In the said method, it is preferred that the organosilicon compound constituents (C) and (D) are selected to satisfy the following formula:
1.3xe2x89xa6log[MFR(C)/MFR(D)]xe2x89xa64.0
preferably the following formula:
1.4xe2x89xa6log[MFR(C)/MFR(D)]xe2x89xa64.0,
more preferably the following formula:
1.6xe2x89xa6log[MFR(C)/MFR(D)]xe2x89xa64.0.
(wherein MFR(C) is a melt flow rate of polypropylene homopolymer obtained by polymerizing propylene in the presence of the constituents (A), (B), and (C), and MFR(D) is a melt flow rate of polypropylene homopolymer obtained by polymerizing propylene in the presence of the constituent (D) in stead of the constituent (C) in the same polymerizing condition as that conducted in the presence of the constituents (A), (B), and (C)),
In the said method, it is preferred that the organosilicon compound constituents (C) and (D) are selected to satisfy the following formulas
0.96 less than [mmmm(D)/mmmm(C)]xe2x89xa61.1 and 96%xe2x89xa6mmmm(D)
(wherein mmmm(C) is an isopentad fraction of polypropylene homopolymer obtained by polymerizing propylene in the presence of the constituents (A), (B), and (C), and mmmm(D) is isopentad fraction of polypropylene homopolymer obtained by polymerizing propylene in the presence of the constituent (D) in stead of the constituent (C) in the same polymerizing condition as that conducted in the presence of the constituents (A), (B), and (C)).
The second aspect of the present invention relates to an xcex1-olefin polymer prepared by the above-mentioned method.
The third aspect of the present invention relates to an xcex1-olefin polymer prepared by polymerizing an xcex1-olefin in the presence of a catalyst containing a solid catalyst constituent (A) which contains magnesium, titanium, a halogen element and an electron donor, an organoaluminum compound constituent (B), an organosilicon compound constituent (C) represented by the above-mentioned general formula (4); and an organosilicon compound constituent (D) represented by the above-mentioned general formulas (5) or (6), wherein a molecular weight distribution in terms of a Mw/Mn ratio is 8 to 20 and a Mz/Mw ratio is 5 to 10 (wherein The Mw/Mn ratio is obtained by calculating from the weight average molecular weight Mw and the number average molecular weight Mn, and the Mz/Mw ratio is obtained by calculating from the Z average molecular weight Mz and the weight average molecular weight Mw, which are measured by means of GPC (gel permeation chromatography) and obtained as the converted values of polystyrene.).
The forth aspect of the present invention relates to an injection molding product having an xcex1-olefin polymer prepared by polymerizing an xcex1-olefin in the presence of a catalyst containing a solid catalyst constituent (A) which contains magnesium, titanium, a halogen element and an electron donor, an organoaluminum compound constituent (B), an organosilicon compound constituent (C) represented by the above-mentioned general formula (4); and an organosilicon compound constituent (D) represented by the above-mentioned general formulas (5) or (6)